Donald Trump's support collapses in 3 of the most important major battlegrounds

Polls in Pennsylvania, Michigan, and New Hampshire suggested that a once tight race in the battlegrounds had shifted in favor of Democratic nominee Hillary Clinton.

The polls showed Clinton with a 9-point lead in Michigan, an 11-point lead in Pennsylvania, and a 17-point lead in New Hampshire. In mid-July, polls conducted in each state found the race to be within 3 points in either direction.

In Michigan, where a Detroit News poll found Clinton to hold about a 9-point lead in a contest that included Libertarian Party nominee Gary Johnson and Green Party nominee Jill Stein, the pollster described "shocking" leads for Clinton in Republican strongholds in the western part of the state.

"He's sitting in the cellar right now, and they're going to have to do something to dramatically turn this around," said Richard Czuba, the president of the Glengariff Group Inc. polling firm. "If I were a Republican running on this ticket right now, I'd be beyond nervous."

The past three polls conducted in Michigan before the Detroit News survey found Clinton with leads of 3 points, 5 points, and 3 points.

"I know that there's a lot of numbers that matter in politics, but Twitter followers still don't trump poll numbers," Michigan Republican strategist Greg McNeilly told the News, referring to Trump's massive social-media following. "He should stick to his stronger, more secure, and more prosperous America message."

Hillary Clinton. Joe Raedle/ Getty Images

The 11-point advantage in Pennsylvania, found in the poll conducted by Franklin & Marshall College, was the largest lead enjoyed by Clinton since late April, before Trump had sealed the GOP nomination. The poll found Clinton with a 49%-to-38% edge among likely voters that expanded to a 48%-to-35% edge among registered voters.

Trump has made a strong push to put Pennsylvania in play this cycle, though the state hasn't voted for a Republican in the presidential race since 1988.

Between May 8 and July 11, just two of seven polls in the state found the race in the Keystone State separated by more than 2 points, according to RealClearPolitics. Since then, Clinton has enjoyed leads of 4, 9, and now 11 points.

Another eye-opening statistic from the poll: Just two in five Pennsylvania voters who watched the Republican convention last month said it made them more likely to vote for Trump. On the other hand, 53% said it made them less likely to do so.

The numbers were virtually flipped for Clinton, as 62% of those who watched last week's Democratic convention — held in Philadelphia — said they were more likely to vote for the former secretary of state. Only 39% said it made them less likely to vote for the Democratic nominee.

The Manhattan billionaire now faces a massive 17-point hole in the Granite State — a state where he was found to be within 2 points in mid-July.

WBUR's poll showed Clinton with a 51%-to-34% advantage over Trump. Just 63% of Republicans said they would vote for their party's nominee, while 86% of Democrats were ready to cast ballots for Clinton.

Thursday brought the latest in a wave of bad polling news for Trump that has shown Clinton to be taking bigger national leads. A Fox News poll released Wednesday found Clinton holding a 10-point lead over the real-estate magnate among voters nationwide.